The use of electronics on vehicles, especially in the area of electronic control systems has been and will continue to increase. For example, electronic engine, transmission, and steering controllers and in the earthmoving vehicle field, electronic implement controllers all are becoming more common and more complex.
Typically, the controller is supplied with data from a number of sensors. As a result of the increasing complexity of such systems, the information or data that the sensors are required to provide also increases in complexity, for example, the amount of information conveyed, the accuracy of the data, the dependability of the data, and the speed at which it is acquired. Today's sensors typically must increase each of these parameters while minimizing overall costs.
One such sensor is used to measure the speed and direction of a rotating shaft. Such information may be required by, for example, an electronic transmission control system. Typically, in order to measure the speed of rotation, a rotor with a plurality of teeth is fixed to the shaft. The rotor rotates with the shaft. A pickup sensor is placed in a suitable position to sense the teeth as the rotor moves beneath it. By counting the teeth and measuring time, the speed of the shaft may be determined. However, measuring the direction of the shaft's rotation is more difficult.
One method for measuring the direction of a shaft's rotation is to use two pickup sensors or sensor elements. The two sensors elements are placed in a particular spatial relationship with the teeth of the rotor. By determining the relative times at which an edge is detected by each sensor element, the direction can be determined. However, this method requires additional hardware and the associated costs of the additional sensor element. In addition, this method also requires addition computational time and/or added circuit complexity in order to process the signals from the two sensor elements.
In another method for measuring the direction of a shaft's rotation is to place a distinguishing feature, e.g., an over or under sized tooth or a missing tooth on the rotor. One such system is disclosed in U.S. Pat. No. 4,972,332 issued Nov. 20, 1990 to Luebbering et al. The apparatus disclosed in Luebbering et al includes a rotor with a plurality of teeth and a distinguishing feature. The distinguishing feature includes one undersized tooth surrounded by "normal" sized teeth and two consecutive undersized teeth separated from the first undersized tooth by three normal teeth. The apparatus detects both the rising and falling edges of the teeth to determine speed and direction of the rotor. The direction of the rotor is determined by identifying the single undersized tooth. If three normal sized teeth followed by two undersized teeth are detected the shaft is rotating in one direction. If not, then the shaft is rotating in the opposite direction.
However with the apparatus in Luebbering, determination of the shaft's direction is dependent upon the detection of the single undersized tooth. That is, in order to determine the shaft's direction, the undersized tooth has to be detected first. It is desirous to provide direction information more consistently, that is, independent of the position of the rotor.
The present invention is adapted to overcome one or more of the problems as set forth above.